Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A projection display device according to the invention includes a
separating unit that assigns X separation information for identifying a
type of an image to each pixel by using a characteristic amount of the
input image, a luminance detecting unit that detects a luminance of a
screen, a first determining unit that determines a first target region
indicating a region on which halftone processing of converting the number
of gradations is performed on the input image by using the X separation
information, and a halftone processing unit that executes the halftone
processing that varies depending on the luminance on the first target
region.

Claims:

1. A projection display device configured to project and display an input
image input from an external device onto a screen, the projection display
device comprising: an assigning unit configured to assign identification
information for identifying a type of an image to each pixel by using a
characteristic amount of the input image; a luminance detecting unit
configured to detect a luminance of the screen; a first determining unit
configured to determine a first target region indicating a region on
which halftone processing of converting the number of gradations is
performed on the input image by using the identification information; and
a halftone processing unit that executes the halftone processing that
varies depending on the luminance on the first target region.

2. The projection display device according to claim 1, wherein the first
determining unit determines a region, as the first target region,
constituted by pixels to which the identification information indicating
highlight as an image of which gradation value is equal to or higher than
a threshold has been assigned on the input image, and the halftone
processing unit executes first dither processing on the first target
region when the luminance is equal to or higher than a reference value
and executes second dither processing, with which lower screen ruling
than the screen ruling with the first dither processing is set, on the
first target region when the luminance is lower than the reference value.

3. The projection display device according to claim 1, wherein the first
determining unit determines a region, as the first target region,
constituted by pixels to which the identification information indicating
a low-contrast character as a character image of which gradation value is
equal to or higher than a threshold has been assigned on the input image,
the halftone processing unit executes first halftone processing on the
first target region when the luminance is equal to or higher than a
reference value and executes second halftone processing on the first
target region when the luminance is lower than the reference value, and
the number of gradations after being converted through the first halftone
processing is smaller than the number of gradations after being converted
through the second halftone processing.

4. The projection display device according to claim 1, further
comprising: a correction unit configured to perform gradation correction
of correcting input/output characteristics of an image; and a second
determining unit configured to determine a second target region on which
the gradation correction is performed on the input image by using the
identification information, wherein the correction unit executes the
gradation correction that varies depending on the luminance on the second
target region.

5. The projection display device according to claim 4, wherein the second
determining unit determines a region, as the second target region,
constituted by pixels to which the identification information indicating
a low-contrast character as a character image of which gradation value is
equal to or higher than a threshold has been assigned on the input image,
and the correction unit executes first gradation correction on the second
target region when the luminance is equal to or higher than a reference
value and executes second gradation correction, with which a bright
portion of the input image becomes darker than with the first gradation
correction, on the second target region when the luminance is lower than
the reference value.

6. The projection display device according to claim 4, further comprising
a control unit configured to control operations of the halftone
processing unit and the correction unit in accordance with bibliographic
information indicating operation conditions of the external device that
outputs image data of a scanned document as the input image.

7. The projection display device according to claim 6, wherein the
control unit does not cause the halftone processing unit and the
correction unit to operate when the bibliographic information indicates a
photograph mode in which an image as an output target is handled as a
photographic image and causes the halftone processing unit and the
correction unit to operate when the bibliographic information indicates a
character mode in which the image as the output target is handled as a
character image.

8. A projection display method of projecting and displaying an input
image input from an external device onto a screen, the projection display
method comprising: assigning identification information for identifying a
type of an image to each pixel by using a characteristic amount of the
input image; detecting a luminance of the screen; determining a target
region indicating a region on which halftone processing of converting the
number of gradations is performed on the input image by using the
identification information; and executing the halftone processing that
varies depending on the luminance on the target region.

9. A computer program product comprising a non-transitory computer-usable
medium having a computer program that causes a computer to execute:
assigning identification information for identifying a type of an image
to each pixel by using a characteristic amount of an input image input
from an external device; detecting a luminance of a screen onto which the
input image is projected and displayed; determining a target region
indicating a region on which halftone processing of converting the number
of gradations is performed on the input image by using the identification
information; and executing the halftone processing that varies depending
on the luminance on the target region.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and incorporates by
reference the entire contents of Japanese Patent Application No.
2012-000127 filed in Japan on Jan. 4, 2012.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a projection display device, a
projection display method, and a computer program.

[0004] 2. Description of the Related Art

[0005] Conventionally, known is a technique of performing preview display
of an image to be printed by a printing device by a projection display
device such as a projector. Japanese Patent Application Laid-open No.
2006-304316 discloses a technique of correcting image data for increasing
output on low-gradation portions (shadow portions) based on color
information and brightness information of a projection screen of the
projector in order to enhance the reproducibility of colors.

[0006] The technique disclosed in Japanese Patent Application Laid-open
No. 2006-304316, however, fails to sufficiently enhance the
reproducibility of colors. For example, the technique disclosed in
Japanese Patent Application Laid-open No. 2006-304316 fails to enhance
the reproducibility on high-gradation portions (highlight portions).

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to at least partially
solve the problems in the conventional technology.

[0008] There is needed to provide a projection display device, a
projection display method, and a computer program that can sufficiently
enhance the reproducibility of colors.

[0009] The above and other objects, features, advantages and technical and
industrial significance of this invention will be better understood by
reading the following detailed description of presently preferred
embodiments of the invention, when considered in connection with the
accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a block diagram illustrating a configuration example of
an information projection system;

[0011]FIG. 2 is a diagram illustrating detailed contents of a data
processing unit;

[0012]FIG. 3 is a table for explaining a method of assigning X separation
information;

[0013]FIG. 4 is a view for explaining an example of extraction of a
region corresponding to each piece of X separation information from an
input image;

[0014]FIG. 5 is a table for explaining a method of switching γ
correction in accordance with the X separation information;

[0015]FIG. 6 is a graph illustrating an example of a γ correction
curve to be used for the γ correction;

[0016]FIG. 7 is a table for explaining a method of switching halftone
processing in accordance with the X separation information and S
luminance information;

[0017]FIG. 8 is a graph illustrating an example of a correspondence
relationship between an input gradation and an output gradation when
simple nine-value processing is applied;

[0018]FIG. 9 is a graph illustrating an example of a correspondence
relationship between an input gradation and an output gradation when
simple four-value processing is applied;

[0019] FIG. 10 is a schematic view illustrating a case when high screen
ruling binary dither processing is applied to a highlight region;

[0020] FIG. 11 is a schematic view illustrating a case when low screen
ruling binary dither processing is applied to the highlight region;

[0021]FIG. 12 is a table for explaining a method of switching γ
correction in accordance with the X separation information and the S
luminance information; and

[0022]FIG. 13 is a graph illustrating an example of a γ correction
curve to be used for second γ correction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, embodiments of a projection display device, a
projection display method, and a computer program according to the
present invention are described in detail with reference to the
accompanying drawings. A projector is described as an example of the
projection display device in the following but the projection display
device is not limited thereto.

A: First Embodiment

[0024]FIG. 1 is a diagram illustrating a schematic configuration example
of an information projection system 1 according to the embodiment. As
illustrated in FIG. 1, the information projection system 1 includes a
projector 100 and a multifunction peripheral (MFP) 101 that is an
external device. The MFP 101 outputs image data of a scanned document to
the projector 100 as an input image. The MFP 101 includes a scanner 109,
a scanner data processing unit 110, a storage device 111, a plotter data
processing unit 112, a plotter 113, and an operating unit 114.

[0025] The scanner 109 scans image data on a document. The scanner data
processing unit 110 performs scanner-correction-type image processing,
such as black correction and shading correction, on the image data
scanned by the scanner 109. The operating unit 114 is an external I/F
that receives input of specification of bibliographic information
indicating operation conditions of the MFP 101. Examples of the
bibliographic information include information specifying a document mode,
the resolution of an image, and the density of an image.

[0026] The scanner data processing unit 110 performs image processing in
accordance with the bibliographic information received by the operating
unit 114 on image data scanned by the scanner 109. The storage device 111
stores image data (image data in an RGB format in this example) after
having been subjected to the image processing by the scanner data
processing unit 110 and the bibliographic information received by the
operating unit 114. The plotter data processing unit 112 performs
plotter-correction-type image processing on the image data stored in the
storage device 111. When the plotter 113 receives the image data on which
the image processing has been performed by the plotter data processing
unit 112, the plotter 113 outputs (outputs on paper) the received image
data onto transfer paper by using an electrophotography process by using
laser beam.

[0027] The projector 100 includes an image input unit 102, a data
processing unit 103, an image output unit 104, a luminance detecting unit
105, a control unit 106, and an operating unit 107. The projector 100 and
the MFP 101, which is an external device, are connected to each other
through network such as a LAN or a USB.

[0028] The image input unit 102 loads the image data (image data in the
RGB format) and the bibliographic information stored in the storage
device 111 of the MFP 101. In the embodiment, as an example, a gradation
of one pixel on each image data in the RGB format that has been loaded by
the image input unit 102 is expressed by 8 bits. That is to say, each
image data in the RGB format that has been loaded by the image input unit
102 is image data of 8 bits. In the following description, the image data
of RGB each having 8 bits that has been loaded by the image input unit
102 is referred to as an "input image".

[0029] The data processing unit 103 performs image processing for
correcting the input image loaded by the image input unit 102 to image
data to be projected onto an image projection screen 108. Detailed
contents of the image processing are described in detail later.

[0030] The image output unit 104 projects (outputs) the image data on
which the image processing by the data processing unit 103 has been
performed onto the image projection screen 108. The image output unit 104
is constituted by including a light source formed by a fixed-type light
source such as a mercury lamp and an LED, a transmission-type liquid
crystal panel, and a projection lens. Light from the light source is
divided into three primary colors (red, blue, green) on the
transmission-type liquid crystal panel and the divided light components
are enlarged by the projection lens so as to be projected onto the image
projection screen 108.

[0031] The luminance detecting unit 105 takes a luminance that is
brightness of reflected light from the image projection screen 108 as
input and converts it to S luminance information. To be more specific,
the luminance detecting unit 105 loads the reflected light from the image
projection screen 108 as the luminance and converts the luminance to a
voltage by a photodiode, for example. Then, the converted voltage is
converted to a digital value (for example, 8 bits) by an A/D converter so
as to obtain the S luminance information.

[0032] The operating unit 107 is a user interface that receives various
types of operation inputs. The control unit 106 controls the projector
100 overall. The control unit 106 is constituted by including a CPU, a
volatile memory such as a RAM to be used for storing data temporarily and
a non-volatile memory such as a ROM and an NVRAM in which programs and
image processing parameters are stored. The CPU of the control unit 106
loads the programs stored in the non-volatile memory and the like and
develops and executes the loaded programs on the volatile memory so as to
control each part of the projector 100. The control unit 106 controls
each part (the image input unit 102, the data processing unit 103, the
image output unit 104, the luminance detecting unit 105, and the like) of
the projector 100 in accordance with contents (bibliographic information)
specified by a user.

[0033] In the information projection system 1 according to the embodiment,
a user can check image data projected onto the image projection screen
108 as a preview image of a print image of the MFP 101 and determine
whether printing by the MFP 101 is executed.

[0034] Next, detailed contents of the data processing unit 103 of the
projector 100 are described with reference to FIG. 2. As illustrated in
FIG. 2, the data processing unit 103 includes a separating unit 201, a
gradation correction unit 202, a magnification changing unit 203, and a
gradation processing unit 204.

[0035] The separating unit 201 calculates characteristic amounts such as a
density value and an edge amount of the input image loaded by the image
input unit 102. Then, the separating unit 201 assigns X separation
information to be used for subsequent image processing to each pixel by
using the calculated characteristic amounts. The X separation information
is identification information for identifying a type of the image. The
separating unit 201 corresponds to an "assigning unit" in the scope of
the present invention. In the embodiment, as illustrated in FIG. 3, the
following five types are prepared as the "X separation information" and
each of them is expressed by data of 4 bits. The five types include a
"low-contrast character" indicating a character image of which gradation
value is equal to or higher than a threshold, a "character" indicating a
character image of which gradation value is lower than the threshold,
"halftone", "highlight" indicating an image of which gradation value is
equal to or higher than the threshold, and "solid" indicating a filled
image.

[0036] The separating unit 201 determines whether a pixel corresponds to
either of white background or non-white background, either of a character
or a non-character, either of halftone or non-halftone, and either of a
bright portion or a non-bright portion for each pixel of the input image.
Note that when the pixel corresponds to the white background, the most
significant bit in the data of 4 bits indicating the X separation
information corresponds to "1", and when the pixel corresponds to the
non-white background, the most significant bit is "0". When the pixel
corresponds to the character, the second significant bit is "1", and when
the pixel corresponds to the non-character, the second significant bit is
"0". When the pixel corresponds to the halftone, the third significant
bit is "1", and when the pixel corresponds to the non-halftone, the third
significant bit is "0". When the pixel corresponds to the bright portion,
the least significant bit is "1", and when the pixel corresponds to the
non-bright portion, the least significant bit is "0". Then, the
separating unit 201 determines whether the pixel corresponds to any of
the "low-contrast character", the "character", the "halftone", the
"highlight", and the "solid" based on the determination result, and
assigns data of 4 bits indicating the corresponding X separation
information to the pixel.

[0037] In the example as illustrated in FIG. 3, for each pixel of the
input image, when the pixel is the character and the bright portion, the
separating unit 201 determines that the pixel corresponds to the
"low-contrast character" and assigns data ("x1x1", note that x may be any
of "0" and "1") of 4 bits indicating the "low-contrast character" to the
pixel. Alternatively, when the pixel is the character and the non-bright
portion, the separating unit 201 determines that the pixel corresponds to
the "character" and assigns data ("x1x0") of 4 bits indicating the
"character" to the pixel. Furthermore, when the pixel is the
non-character and the halftone, the separating unit 201 determines that
the pixel corresponds to the "halftone" and assigns data ("x01x") of 4
bits indicating the "halftone" to the pixel. In addition, when the pixel
is the white background, the non-character, and the non-halftone, the
separating unit 201 determines that the pixel corresponds to the
"highlight" and assigns data ("100x") of 4 bits indicating the
"highlight" to the pixel. Furthermore, when the pixel is the non-white
background, the non-character, and the non-halftone, the separating unit
201 determines that the pixel corresponds to the "solid" and assigns data
("000x") of 4 bits indicating the "solid" to the pixel.

[0038] As described above, the separating unit 201 assigns the X
separation information to each pixel of the input image. With this, as
illustrated in FIG. 4, the separating unit 201 can extract a region
formed by pixels to which the X separation information indicating the
"low-contrast character" has been assigned on an input image 231 as a
"low-contrast character region 233". In the same manner, the separating
unit 201 can extract a region formed by pixels to which the X separation
information indicating the "character" has been assigned on the input
image 231 as a "character region 232". The separating unit 201 can
extract a region formed by pixels to which the X separation information
indicating the "halftone" has been assigned on the input image 231 as a
"halftone region 234". The separating unit 201 can extract a region
formed by pixels to which the X separation information indicating the
"highlight" has been assigned on the input image 231 as a "highlight
region 235". Moreover, the separating unit 201 can extract a region
formed by pixels to which the X separation information indicating the
"solid" has been assigned on the input image 231 as a "solid region 236".

[0039] Then, the separating unit 201 transmits the X separation
information of each pixel on the input image to each of the gradation
correction unit 202 and the gradation processing unit 204.

[0040] Description is continued with reference to FIG. 2, again. The
gradation correction unit 202 includes a second determining unit 207 and
a correction unit 208. The second determining unit 207 determines a
region (referred to as "second target region") on which gradation
correction (in this example, γ correction) for correcting
input/output characteristics of an image is performed on the input image
by using the input image, the bibliographic information, S luminance
information from the luminance detecting unit 105, and the X separation
information from the separating unit 201 as inputs. As illustrated in
FIG. 5, in the embodiment, the second determining unit 207 determines the
region (low-contrast character region 233) formed by the pixels to which
the X separation information indicating the "low-contrast character" has
been assigned on the input image as the second target region.

[0041] The correction unit 208 performs the γ correction on the
second target region determined by the second determining unit 207. It is
to be noted that the correction unit 208 does not perform the γ
correction on regions other than the low-contrast character region 233 on
the input image to skip them. FIG. 6 is a graph illustrating an example
of a γ correction curve to be used for the γ correction by
the correction unit 208. The projector 100 has a characteristic that a
bright portion of the image is difficult to be reproduced. Therefore,
γ correction for making the bright portion on the input image data
be slightly darker is applied to the low-contrast character region 233.
To be more specific, as illustrated in FIG. 6, the γ correction
curve is set such that a change ratio of a gradation value of output when
a gradation value of input is equal to or higher than a threshold d is
lower than a change ratio of a gradation value of output when the
gradation value of input is lower than the threshold d.

[0042] Description is continued with reference to FIG. 2, again. The
magnification changing unit 203 performs magnification change of a
resolution of the input image to a resolution received on the operating
unit 107 of the projector 100 (resolution specified by a user). The
magnification changing unit 203 performs a convolution operation or the
like in the main scanning direction and the sub scanning direction on a
resolution of the image scanned by the MFP 101 so as to execute
magnification changing processing of contraction or enlargement in order
to make the resolution match with a resolution of the projector 100 with
reference to the bibliographic information.

[0043] The gradation processing unit 204 includes a first determining unit
205 and a halftone processing unit 206. The first determining unit 205
determines a region (referred to as "first target region") on which
halftone processing of converting the number of gradations is performed
on the input image by using the input image, the S luminance information
from the luminance detecting unit 105, and the X separation information
from the separating unit 201 as inputs. As illustrated in FIG. 7, in the
embodiment, the first determining unit 205 determines a region
(low-contrast character region 233) formed by the pixels to which the X
separation information indicating the "low-contrast character" has been
assigned and the region (highlight region 235) formed by the pixels to
which the X separation information indicating the "highlight" has been
assigned on the input image as the first target regions.

[0044] The halftone processing unit 206 executes the halftone processing
that varies depending on the S luminance information on the first target
regions. Description thereof is made more in detail below. At first,
contents of the halftone processing to be executed on the low-contrast
character region 233 are described. The halftone processing unit 206
applies simple nine-value processing as illustrated in FIG. 8 to the
low-contrast character region 233 when the luminance indicated by the S
luminance information is lower than a reference value (in the case of
being "dark").

[0045] On the other hand, the halftone processing unit 206 applies simple
four-value processing as illustrated in FIG. 9 to the low-contrast
character region 233 when the luminance indicated by the S luminance
information is equal to or higher than the reference value (in the case
of being "bright"). When the luminance indicated by the S luminance
information is equal to or higher than the reference value (in the case
of being "bright"), image visibility of the image is bad even when the
simple nine-value processing is executed. Therefore, in this case, the
processing is switched to the simple four-value processing so as not to
use the bright portion to the extent possible. With this, the
low-contrast character at the bright side is not lacked and the density
becomes even, so that visibility when the image is displayed on the
projector 100 is improved.

[0046] In the embodiment, the halftone processing unit 206 applies the
simple four-value processing to the low-contrast character region 233
when the luminance indicated by the S luminance information is equal to
or higher than the reference value. On the other hand, the halftone
processing unit 206 applies the simple nine-value processing to the
low-contrast character region 233 when the luminance indicated by the S
luminance information is lower than the reference value. However, the
processing is not limited thereto. In summary, it is sufficient that the
halftone processing unit 206 executes first halftone processing on the
low-contrast character region 233 when the luminance is equal to or
higher than the reference value while the halftone processing unit 206
executes second halftone processing on the low-contrast character region
233 when the luminance is lower than the reference value. In this case,
the number of gradations (in the embodiment, "4") after being converted
through the first halftone processing is smaller than the number of
gradations (in the embodiment, "9") after being converted through the
second halftone processing.

[0047] Next, contents of the halftone processing to be executed on the
highlight region 235 are described. Note that the projector 100 has the
characteristic that a bright portion of an image is difficult to be
reproduced. There arises a risk that white spots are generated when a
gradation value of each pixel included in the highlight region 235 is
output as it is. In order to avoid the risk, in the embodiment, dither
processing with which multiple-valued image data is binarized is applied
to the highlight region 235. With this, the density is expressed by an
area of all black portions (a gradation is expressed by crude density of
dots of "black"). Therefore, the reproducibility of highlight is
improved. It is to be noted that when the luminance of the image
projection screen 108 is equal to or higher than the reference value (in
the case of being "bright"), the image is not influenced by environmental
light therearound easily. Therefore, even when the dots of the dither
processing are small, the visibility of the dots does not become bad.
Therefore, the halftone processing unit 206 in the embodiment applies
dither processing (high screen ruling binary dither processing) with
which the high screen ruling is set is applied to the highlight region
235 when the luminance indicated by the S luminance information is equal
to or higher than the reference value while taking the resolution and the
like of the image into consideration.

[0048] FIG. 10 is a schematic view illustrating a case when the high
screen ruling binary dither processing is applied to the highlight region
235.

[0049] On the other hand, when the luminance indicated by the S luminance
information is lower than the reference value (in the case of being
"dark"), the luminance of the image projection screen 108 is dark. This
indicates that a distance between the projector 100 and the image
projection screen 108 is large. In this case, the image is influenced by
environmental light therearound easily. Therefore, the projector 100 is
difficult to reproduce the bright portion of the image. In this case,
when the dots of the dither processing are small, the visibility of the
dots becomes bad and the highlight cannot be reproduced sufficiently.
Accordingly, while giving priority to reproduction of the highlight, the
halftone processing unit 206 in the embodiment applies dither processing
(low screen ruling binary dither processing) with which the low screen
ruling is set is applied to the highlight region 235 when the luminance
indicated by the S luminance information is lower than the reference
value. FIG. 11 is a schematic view illustrating a case when the low
screen ruling binary dither processing is applied to the highlight region
235.

[0050] In the embodiment, the halftone processing unit 206 applies the
high screen ruling binary dither processing to the highlight region 235
when the luminance indicated by the S luminance information is equal to
or higher than the reference value. On the other hand, the halftone
processing unit 206 applies the low screen ruling binary dither
processing to the highlight region 235 when the luminance indicated by
the S luminance information is lower than the reference value. However,
the processing is not limited thereto. The number of gradations and the
screen ruling to be converted by the dither processing can be set
arbitrarily. In summary, it is sufficient that the halftone processing
unit 206 executes first dither processing on the highlight region 235
when the luminance is equal to or higher than the reference value while
the halftone processing unit 206 executes second dither processing, with
which lower screen ruling than that with the first dither processing is
set, on the highlight region 235 when the luminance is lower than the
reference value.

[0051] As described above, in the embodiment, the halftone processing that
varies depending on the luminance indicated by the S luminance
information is executed on the first target region, so that the
reproducibility of colors of an image to be projected onto the image
projection screen 108 can be enhanced, thereby obtaining advantageous
effects.

B: Second Embodiment

[0052] The embodiment is different from the above-mentioned first
embodiment in a point that the correction unit 208 executes γ
correction that varies depending on the luminance indicated by the S
luminance information on the low-contrast character region 233.
Descriptions of parts that are common to those in the first embodiment
are omitted appropriately.

[0053] As illustrated in FIG. 12, the correction unit 208 executes first
γ correction on the low-contrast character region 233 when the
luminance indicated by the S luminance information is equal to or higher
than the reference value (in the case of being "bright"). On the other
hand, the correction unit 208 executes second γ correction on the
low-contrast character region 233 when the luminance indicated by the S
luminance information is lower than the reference value (in the case of
being "dark"). In the first γ correction, the γ correction
curve as illustrated in FIG. 6 is used. On the other hand, in the second
γ correction, a γ correction curve as illustrated in FIG. 13
is used. As described above, when the luminance indicated by the S
luminance information is lower than the reference value (in the case of
being "dark"), an image is influenced by environmental light therearound
easily and the projector 100 is difficult to reproduce a bright portion
of the image further. Therefore, the second γ correction, with
which the bright portion of the input image data is darker than with the
first γ correction, is applied to the low-contrast character region
233. To be more specific, as illustrated in FIG. 13, the γ
correction curve to be used for the second γ correction is set such
that a change ratio of a gradation value of output when a gradation value
of input is equal to or higher than a threshold d is lower than a change
ratio of a gradation value of output when the gradation value of input is
lower than the threshold d. Furthermore, the change ratio of the
gradation value of output when the gradation value of input is equal to
or higher than the threshold d is set to be lower than that of the
γ correction curve (see, FIG. 6) to be used for the first γ
correction.

[0054] In the above-mentioned embodiments, the control unit 106 causes the
gradation correction unit 202 and the gradation processing unit 204 to
operate in accordance with the above-mentioned bibliographic information.
To be more specific, the control unit 106 does not cause the gradation
correction unit 202 and the gradation processing unit 204 to operate when
the bibliographic information indicates a photograph mode in which an
image as an output target is handled as a photographic image. That is to
say, the projector 100 does not perform any operation. On the other hand,
the control unit 106 controls each of the gradation correction unit 202
and the gradation processing unit 204 so as to perform operations as
described in the above-mentioned first embodiment or second embodiment
when the bibliographic information indicates a character mode in which
the image as the output target is handled as a character image. The MFP
101 and the projector 100 cooperate with each other such that processing
on the projector 100 is made different depending on an image quality mode
of the MFP 101. Therefore, a scan image can be reflected as it is and
settings of the projector 100 can be omitted.

[0055] Hereinbefore, embodiments of the present invention have been
described. However, the present invention is not limited to the
above-mentioned embodiments and various modifications can be made in a
range without departing from the scope of the present invention.

[0056] Control programs to be executed in the control unit 106 according
to the above-mentioned embodiments may be configured to be provided by
being recorded in a recording medium that can be read by a computer, such
as a compact disc read only memory (CD-ROM), a flexible disk (FD), a CD
recordable (CD-R), or a digital versatile disk (DVD), in a format that
can be installed or a file that can be executed.

[0057] Furthermore, the control programs to be executed in the control
unit 106 according to the above-mentioned embodiments may be configured
to be provided by being stored on a computer connected to network such as
the Internet and being downloaded through the network. Alternatively, the
control programs to be executed in the control unit 106 according to the
above-mentioned embodiments may be provided or distributed through
network such as the Internet.

[0058] The present invention can provide an advantageous effect of
providing a projection display device, a projection display method, and a
computer program that can sufficiently enhance the reproducibility of
colors.

[0059] Although the invention has been described with respect to specific
embodiments for a complete and clear disclosure, the appended claims are
not to be thus limited but are to be construed as embodying all
modifications and alternative constructions that may occur to one skilled
in the art that fairly fall within the basic teaching herein set forth.